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United States Patent |
5,650,512
|
Ahlem
,   et al.
|
July 22, 1997
|
Fluorescent labeling reagents
Abstract
A class of sulforhodamine labeling reagents capable of binding with a
biomolecular species to produce a conjugate with fluorescent properties.
The sulforhodamine labeling reagents have the structure:
##STR1##
The group X is selected from an alkyl, an olefin, a monocyclic aliphatic
saturated hydrocarbon, an aryl, or nothing at all. The group Y is selected
from an amide, a substituted amide, or nothing at all. The group Z is
selected from a monocyclic aliphatic hydrocarbon, an aryl, or an alkyl, as
defined with respect to group X, a polyethylene glycol chain of the
general form (CH.sub.2 CH.sub.2 O).sub.n, or nothing at all. The alkyl or
polyethylene glycol chain may further have inert intermediate amide,
ether, or disulfide functionalities. The group X, group Y, and group Z
cannot all be nothing at all or non-existent. The group R is an
electrophilic moiety suitable for conjugation of the fluorescent labeling
reagent with a biomolecular species. Also disclosed is a method of making
the reagents.
Inventors:
|
Ahlem; Clarence N. (Bellevue, WA);
Torkelson; Steven M. (San Mateo, CA)
|
Assignee:
|
Systemix (Palo Alto, CA)
|
Appl. No.:
|
484961 |
Filed:
|
June 7, 1995 |
Current U.S. Class: |
546/37 |
Intern'l Class: |
C07D 491/22 |
Field of Search: |
546/37
436/91,96,97,172
|
References Cited
U.S. Patent Documents
4609689 | Sep., 1986 | Schwartz et al. | 523/202.
|
4713348 | Dec., 1987 | Ullman | 435/7.
|
4745181 | May., 1988 | Law et al. | 530/391.
|
5441935 | Aug., 1995 | Rozengurt et al. | 514/15.
|
5453517 | Sep., 1995 | Kuhn et al. | 549/227.
|
Other References
Titus, J.A. et al J. Immunol. Meth. 1982, 50, page 193-204.
Edwards, R.J. et al J. Immunol. Meth. 1989, 117, pp. 215-220.
Abuelyaman, A.S. et al Bioconjugate Chem. 1994, 5, pp. 400-405.
|
Primary Examiner: Ivy; C. Warren
Assistant Examiner: Dahlen; Garth M.
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman
Claims
What is claimed is:
1. A method for preparing a molecular probe, comprising the steps of:
condensing sulforhodamine 101 with phosphorous oxychloride to form product
P1:
##STR11##
condensing product P1 with H.sub.2 NXNH.sub.2 wherein X is selected from
an acyclic saturated aliphatic straight or branched chain hydrocarbon, an
olefin, a monocyclic aliphatic saturated hydrocarbon, or an aryl, wherein
aryl denotes an aromatic ring, a substituted aromatic ring, and fused
aromatic rings, to form product P2:
##STR12##
condensing product P2 with a disuccinimidyl ester, a succinimidyl ester
with a maleimide moiety, a succinimidyl ester with a diimidazolide, or a
succinimidyl ester with a pyridyl disulfide to form products, P3a, 3b, 3c,
3d, respectively:
##STR13##
wherein Z is selected from a monocyclic aliphatic hydrocarbon, an aryl,
and alkyl, or a polyethylene glycol chain of the general formula (CH.sub.2
CH.sub.2 O)n, wherein n=1-3, or nothing at all, wherein said alkyl or
polyethylene glycol chain may further have inert intermediate amide,
disulfide, or ether functionalities.
2. A method for preparing a molecular probe, comprising the steps of:
condensing sulforhodamine 101 with phosphorous oxychloride to form product
P1:
##STR14##
condensing product P1 with H.sub.2 NXNH.sub.2, wherein X is selected from
an acyclic saturated aliphatic straight or branched chain hydrocarbon, an
olefin, a monocyclic aliphatic saturated hydrocarbon, or an aryl, wherein
aryl denotes an aromatic ring, a substituted aromatic ring, and fused
aromatic rings, to form product P2:
##STR15##
condensing product P2 with an acid anhydride of the general formula
Z(CO).sub.2 O, wherein Z is selected from a monocyclic aliphatic
hydrocarbon, an aryl, or an alkyl or polyethylene glycol chain of the
general formula (CH.sub.2 CH.sub.2 O)n, wherein n=1-3, to yield product
P3:
##STR16##
condensing product P3 with a disuccinimidyl carbonate or
N-hydroxysuccinimide (NHS) and a carbodiimide.
Description
FIELD OF THE INVENTION
The present invention relates to the field of fluorophores and to the field
of conjugation of biomolecules with reactive probes for labeling and study
of cytometry, and more particularly to a class of sulforhodamine labeling
reagents and methods of making such reagents.
BACKGROUND OF THE INVENTION
The chemical modification of proteins, nucleotides, and other biomolecules
is an important research tool in immunology, histochemistry, biochemistry,
and cell biology. Conjugation is a form of modification in which two or
more molecules with distinct properties are joined so that some of the
characteristics of each joined molecule are retained in the product. For
example, molecules with special properties of fluorescence or binding
specificity can be covalently bound or conjugated to a protein, DNA
strand, or other biomolecule. Proteins, peptides, polysaccharides,
hormones, nucleic acids and their analogs, and liposomes may be conjugated
with each other or with molecular groups that add useful properties (e.g.,
drugs, radionuclides, toxins, fluorphores, photoprobes, inhibitors,
enzymes, haptens, ligands).
Fluorescent dyes are routinely conjugated to biological molecules to impart
the properties of light absorption and fluorescence to the biomolecule for
a variety of purposes including separation and fluorescence imaging. For
example, fluorescent labeling of antibody molecules is used extensively
for applications such as immunohistological staining and cell separation
by flow cytometry.
The chemical modification of biomolecules with fluorescent probes generally
involve covalent attachment of the probe to the biomolecule, although many
fluorophore probes for nucleic acids do not covalently bond to the target
biomolecule. The most commonly exploited conjugation points for covalent
bonding in proteins are the aliphatic amine groups, notably, the
.epsilon.-amine groups of lysine and the .alpha.-amino groups of the
N-terminal amino acids. Other conjugation points in proteins include thiol
residues in cysteine and cystine, the phenolic hydroxyl group of tyrosine
and carboxlic acid groups of aspartic acid and glutamic acid.
Fluorescent probes are chosen based upon their physical properties. The
probe must be able to bind to a particular site on a biomolecule (i.e.,
amine or thiol group of a protein) and must be relatively specific for
that particular binding site. A probe that is too reactive in the
conjugation reaction solution (e.g. an aqueous solution) will hydrolyze
before binding to the target site. In most cases, the fluorescent probe
should also be relatively soluble in water so as not to precipitate out of
solution and also be capable of reacting rapidly and specifically with a
particular binding site at substantially neutral pH (and particularly
physiological pHs).
The reaction kinetics of a fluorescent probe should be controllable. In
other words, the amount of fluorescent label conjugated per biomolecule
should be capable of being regulated. Regulation of the reaction kinetics
is important to permit consistent reproducibility of labeling results.
Regulation is also important because excess labeling can alter the
biological characteristics of the biomolecule, e.g., it may lower the
biomolecule's affinity for its target. In the case of labeling antibodies,
for example, excessive substitution of the fluorescent probe to the
antibody can reduce the affinity of the antibody for a particular antigen.
The fluorescent probe should have a relatively large extinction
coefficient, that characterizes its light-absorbing power, at least in
certain uses (e.g. fluorescent flow cytometry). The quantum yield should
be large when the probe is bound to the target and is in the solvent
environment where the fluorescence measurement is to be made. The
fluorescent probe should also excite at desired wavelength levels,
preferably above 500 nanometers to avoid autofluorescence from cell
constituents. The photostability, or the number of excitations that a
fluorescent probe can withstand is also important, especially for
detecting a small number of probes in solution.
Common fluorescent labels include fluoroscein and rhodamines. Fluorescein
has a relatively high extinction coefficient and quantum yield, and is
generally soluble in aqueous solutions and easily conjugated to proteins.
However, fluorescein is relatively photounstable and loses fluorescence
below pH 8. Unfortunately, it is preferred to use a pH below 8 when a
probe is conjugated to a protein in a living cell, and consequently
fluoroscein's use in this context has some disadvantages. Fluorescein also
has a wavelength of excitation in a region that produces autofluorescence.
Rhodamines excite in the 500 to 600 nanometer range, where less
autofluorescence is generated. Rhodamines are more photostable than
fluorescein and are pH insensitive under physiological conditions (pH
7-8). However, rhodamines have a relatively low quantum yield and limited
solubility.
One of the most widely used rhodamines for amine-reactive fluorescent
labeling is a sulfonyl halide derivative of rhodamine, sulforhodamine 101
acid chloride, or Texas Red (a trademark of Molecular Probes, Inc.).
Sulforhodamine 101 compounds like Texas Red are particularly useful as
fluorescent dyes since their spectra minimally overlap the spectra of
fluorescein and other green dyes. Typically, sulforhodamine101 compounds
exhibit fluorscence in the wavelength range of 610-630 nanometer. In
comparison, fluorescein has a wavelength of exitation in the range of
500-520 nanometers. Therefore, fluorescein and sulforhodamine 101 are
well-suited for two-color imaging and cell sorting.
Texas Red forms stable sulfonamide bonds that make it a popular
amine-modifying reagent and thus it has proven to be very useful to label
lysine groups on proteins and polypeptides generally. However, sulfonyl
halides, like Texas Red, are highly reactive, are less specific, and
hydrolyze easily prior to conjugation to the target site. Texas Red not
only selectively reacts with amines, but also, through a competing
reaction, tends to react with the solvent medium.
Further, the labeling of proteins with Texas Red is not kinetically
controllable. The labeling results cannot be consistently reproduced and
it is impossible to maintain the substitution ratio of Texas Red to
biomolecule in any desired range depending on input ratios. Instead, the
substitution ratio of Texas Red on a protein depends on intangibles like
stir rate, order of mixing, and the size of the reaction particles.
Thus, there is a need for a rhodamine fluorescent probe that is kinetically
controllable, is site specific but only moderately reactive, and will not
hydrolyze too rapidly.
##STR2##
SUMMARY AND OBJECTS OF THE INVENTION
The invention relates to a novel class of fluorescent labeling reagents for
conjugation to biomolecules. More specifically, the invention relates to a
class of sulforhodamine labeling reagents that are desirable entities for
biomolecular conjugation because the reagents can react rapidly,
controllably, and specifically with target sites at near neutral pH
without organic solvents. Unlike all other sulforhodamine labeling
reagents that are extremely reactive and susceptible to hydrolysis, the
reagents of the instant invention possess sufficient stability in aqueous
solution to allow kinetic control of the conjugation reaction. Thus,
optimal substitution ratios can be achieved and the results can be
reproduced. Finally, the invention relates to the preparation of the
labeling reagents described herein.
Labeling reagents suitable for the conjugation of a biomolecular species
for the purpose of incorporating fluorescent properties have the general
formula:
##STR3##
The group X is selected from an alkyl, an olefin, a monocyclic aliphatic
saturated hydrocarbon, an aryl, or nothing at all. Alkyl denotes an
acyclic saturated aliphatic straight or branched chain hydrocarbon.
--CH.sub.2, --CH.sub.2 CH.sub.2, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 --
are examples of alkyls. A reasonably long alkyl chain (e.g., an alkyl
chain of 5-10 carbon equivalents in length) may be used at group X because
the overall reagent molecule is a zwiterion. An olefin denotes an
unsaturated aliphatic hydrocarbon having the general formula C.sub.n
H.sub.2n. --CH.sub.2 CH.dbd.CHCH.sub.2 -- is an example of an olefin. An
example of a monocyclic aliphatic saturated hydrocarbon is cyclohexane. An
aryl is used to denote an aromatic ring, a substituted aromatic ring, and
fused aromatic rings. Phenyl, hydroxyphenyl, and napthalene are examples
of aryls.
The group Y is selected from an amide, a substituted amide, or an amide
functional moiety, or nothing at all. An example of an amide is NHCO. An
example of a substituted amide is N(CH.sub.3)CO. The amide or substituted
amide may be synthesized from an amide functional moiety such as an
imidazole.
The group Z is selected from a monocyclic aliphatic hydrocarbon, an aryl,
an alkyl or a polyethylene glycol chain of the general form (CH.sub.2
CH.sub.2 O).sub.n, or nothing at all. The alkyl or polyethylene glycol
chain may further have inert intermediate functionalities, e.g., amide,
ether, or disulfide functionalities. Again, a reasonably long alkyl or
polyethylene glycol chain may be used at group X because the overall
reagent molecule is a zwiterion.
Groups X, Y, and Z can all be nothing or non-existent. However, groups X,
Y, and Z cannot be nothing or non-existent at the same time. For example,
an embodiment is contemplated where group X and group Y are nothing or do
not exist, but group Z does exist in the form of a monocyclic aliphatic
hydrocarbon, an aryl, an alkyl or a polyethylene glycol chain of the
general form (CH.sub.2 CH.sub.2 O).sub.n.
The group R is an electrophilic moiety suitable for conjugation of the
fluorescent labeling reagent with a biomolecular species. Included as
acceptable R groups are reactive esters, reactive amides, reactive
disulfides, and maleimide functionalities.
Other objects, features, and advantages of the present invention will be
apparent from the accompanying drawings and from the the detailed
description that follows below.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not limitation
in the figures of the accompanying drawings, in which like references
indicate similar elements and in which:
FIG. 1 illustrates the synthesis of an amine-reactive NHS ester fluorescent
labeling reagent of General Formula I, wherein X is CH.sub.2 CH.sub.2, Y
is NHCO, Z is CH.sub.2 CH.sub.2 CH.sub.2, and R is NHS ester.
FIG. 2 illustrates the synthesis of an amine-reactive NHS ester fluorescent
labeling reagent of General Formula I, wherein X is CH.sub.2 CH.sub.2
CH.sub.2 CH.sub.2, Y is NHCO, Z is CH.sub.2 CH.sub.2 CH.sub.2, and R is
NHS ester.
FIG. 3 illustrates the synthesis of a amine-reactive NHS ester fluorescent
labeling reagent of General Formula I, wherein X is nothing, Y is NHCO, Z
is CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2, and R is NHS ester.
FIG. 4 illustrates the synthesis of thiol-reactive maleimide fluorescent
labeling reagent of General Formula I, wherein X is CH.sub.2 CH.sub.2, Y
is NHCO, Z is cyclohexane, and R is a maleimide moiety.
FIG. 5 illustrates the synthesis of a reactive disulfide fluorescent
labeling reagent of General Formula I, wherein X is CH.sub.2 CH.sub.2, Y
is NHCO, Z is CH.sub.2 CH.sub.2 and R is a pyridyl disulfide.
FIG. 6 illustrates the synthesis of a reactive amide fluorescent labeling
reagent of General Formula I, wherein X is CH.sub.2 CH.sub.2, Y is NHCO, Z
is CH.sub.2 CH.sub.2 CH.sub.2 and R is a substituted amide containing an
imidazole moiety.
FIG. 7 illustrates the synthesis of an amine-reactive NHS ester fluorescent
labeling reagent of General Formula I, wherein X is CH.sub.2
CH.dbd.CHCH.sub.2, Y is NHCO, Z is CH.sub.2 CH.sub.2 CH.sub.2, and R is
NHS ester.
DETAILED DESCRIPTION
Labeling reagents suitable for the conjugation of a biomolecular species
for the purpose of incorporating fluorescent properties have the general
formula:
##STR4##
The group X is selected from an alkyl, an olefin, a monocyclic aliphatic
saturated hydrocarbon, an aryl, or nothing at all. Alkyl denotes an
acyclic saturated aliphatic straight or branched chain hydrocarbon.
--CH.sub.2, --CH.sub.2 CH.sub.2, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 --
are examples of alkyls. A reasonably long alkyl chain may be used at group
X because the overall reagent molecule is a zwiterion. --CH.sub.2
CH.dbd.CHCH.sub.2 -- is an example of an olefin. An example of a
monocyclic aliphatic saturated hydrocarbon is cyclohexane. An aryl is used
to denote an aromatic ring, a substituted aromatic ring, and fused
aromatic rings. Phenyl, hydroxyphenyl, and napthalene are examples of
aryls.
The group Y is selected from an amide, a substituted amide, or nothing at
all. An example of an amide is NHCO. An example of a substituted amide is
N(CH.sub.3)CO.
The group Z is selected from a monocyclic aliphatic hydrocarbon, an aryl,
an alkyl or a polyethylene glycol chain of the general form (CH.sub.2
CH.sub.2 O).sub.n, or nothing at all. The alkyl or polyethylene glycol
chain may further have inert intermediate functionalities, e.g., amide,
ether, or disulfide functionalities. Again, a reasonably long alkyl chain
may be used at group X because the overall reagent molecule is a
zwiterion.
Groups X, Y, and Z can all be nothing or non-existent. However, groups X,
Y, and Z cannot be nothing or non-existent at the same time. For example,
an embodiment is contemplated where group X and group Y are nothing or do
not exist, but group Z does exist. in the form of a monocyclic aliphatic
hydrocarbon, an aryl, an alkyl or a polyethylene glycol chain of the
general form (CH.sub.2 CH.sub.2 O).sub.n.
The group R is an electrophilic moiety suitable for conjugation of the
fluorescent labeling reagent with a biomolecular species. Included as
acceptable R groups are reactive esters, reactive amides, reactive
disulfides, and substituted amide's containing maleimide functionalities.
Suitable biomolecular species include proteins, peptides, hormones,
oligonucleotides (RNA, DNA) and other nucleotides and their analogs, and
liposomes.
Synthesis of the Sulforhodamine 101 Fluorescent Labeling Reagent
As illustrated in FIGS. 1 through 7, reagents of General Formula I, wherein
X is selected from an alkyl, an olefin, a monocyclic aliphatic saturated
hydrocarbon, an aryl, or nothing (e.g., X=0,1,2, . . . carbon equivalents
in length), and Y is an amide are prepared by condensation of
sulforhodamine 101 with a compound of the general formula H.sub.2
N--X--NH.sub.2 followed by condensation with an NHS-ester derivative or
reactive amide of the general formulas:
##STR5##
wherein Z is selected from a monocyclic aliphatic hydrocarbon, an aryl, an
alkyl, as defined with respect to group X, a polyethylene glycol chain of
the general form (CH.sub.2 CH.sub.2 O).sub.n, or nothing at all. The alkyl
or polyethylene glycol chain may further have inert intermediate amide,
disulfide, or ether functionalities. Group R is an electrophilic moiety
suitable for conjugation of the fluorescent labeling reagent with a
biomolecular species.
The synthesis of the labeling reagent of General Formula I is accomplished
as follows. Sulforhodamine 101 is mixed with freshly distilled phosphorous
oxychloride. The mixture is stirred slightly overnight. The phosphorous
oxychloride is then removed at a vacuum pump to dryness. The
sulforhodamine 101 is then dissolved in dry dimethyl formamide (DMF).
A diamine compound of the general formula H.sub.2 N--X--NH.sub.2 is
separately mixed with an amount of dry DMF. The sulforhodamine 101/DMF
mixture is then added dropwise to the diamine mixture with vigorous
stirring. The solution is then allowed to stir for 15 minutes. The
solvents are then evaporated at the pump to dryness, and the residue is
taken up in a few milliliters of methanol and partitioned between water
and chloroform in a separatory funnel. The water layer is extracted three
times with chloroform and the organic extracts are combined, dried,
evaporated, and pumped dry to give the crude amine.
The crude amine is dissolved in chloroform and developed on two preparative
TLC plates (1 mm thickness). After separation of the bottom amine band
from the plate, the adsorbent is extracted four times with methanol and
once overnight. The extracts are combined, reduced in volume, and poured
into water. Upon extraction with chloroform, the dye solution is dried,
filtered, evaporated, and pumped dry to yield a sulforhodamine 101
sulfonyl diamine of the general formula:
##STR6##
wherein X is selected from an alkyl, an olefin, a monocyclic aliphatic
saturated hydrocarbon, an aryl, or nothing. Alkyl denotes an acyclic
saturated aliphatic straight or branched chain hydrocarbon. --CH.sub.2,
--CH.sub.2 CH.sub.2 --, --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 -- are
examples of alkyls. --CH.sub.2 CH.dbd.CHCH.sub.2 -- is an example of an
olefin. An example of a monocyclic aliphatic saturated hydrocarbon is
cyclohexane. An aryl is used to denote an aromatic ring, a substituted
aromatic ring, and fused aromatic rings. Phenyl, hydroxyphenyl, and
napthalene are examples of aryls.
The sulforhodamine 101 sulfonyl diamine in DMF is inversely added under
vigorous stirring to a NHS ester compound of the general formula:
##STR7##
wherein Z is selected from a monocyclic aliphatic hydrocarbon, an aryl, an
alkyl, as defined with respect to group X, a polyethylene glycol chain of
the general form (CH.sub.2 CH.sub.2 O).sub.n, or nothing at all. The alkyl
or polyethylene glycol chain of group Z may further have inert
intermediate amide, disulfide, or ether functionalities. Group R is an
electrophilic moiety suitable for conjugation of the fluorescent labeling
reagent with a biomolecular species. Included as acceptable R groups are
reactive esters, reactive amides, maleimides, and reactive disulfides.
Example of reactive esters are NHS esters. Examples of reactive amides
include imidazole functionalities. Examples of reactive disulfides include
pyridyl disulfides.
The sulforhodamine 101 sulfonyl diamine/NHS ester solution is stirred for
15 minutes then evaporated in vacuo. The residue is taken up in chloroform
and applied to four preparative TLC plates (1 mm thickness) with 15%
MeOH/CHCl.sub.3 as the eluant. The portion of the plate containing the
product is removed and quickly exhaustively extracted with 15%
MeOH/CHCl.sub.3. The 15% MeOH/CHCl.sub.3 solution is evaporated and the
residue is dissolved in ethanol-free chloroform. The mixture is filtered,
evaporated, and pumped dry to yield the product of General Formula I.
Alternatively, the product of General Formula I wherein group R is a
reactive ester may be synthesized by dissolving the sulforhodamine 101
sulfonyl diamine of the general formula
##STR8##
in dry pyridine followed by the addition of an acid anhydride of the
general formula Z(CO).sub.2 O, wherein Z is selected from a monocyclic
aliphatic hydrocarbon, an aryl, or an alkyl, as defined with respect to
group X, or a polyethylene glycol chain of the general form (CH.sub.2
CH.sub.2 O).sub.n. The alkyl or polyethylene glycol chain of group Z may
further have inert intermediate amide, disulfide, or ether
functionalities. The solution is allowed to stir for 15 minutes followed
by the removal of the pyridine by evaporation. The residue is
chromatographed on a silica gel column by dissolving it in a solution
consisting of 10% MeOH/89.5% CH.sub.3 Cl/)0.5% HOAc. The first fraction is
eluted with this solvent mixture. When it has been cleared from the
column, the acid fraction is chased through with 30% MeOH/69% CH.sub.3
Cl/1% HOAc and collected and the solvents are pumped dry to yield an acid
of the general formula:
##STR9##
To this acid is combined an electrophilic compound R', wherein R' is
selected from the group consisting of N-hydroxysuccinimido derivatives and
N-hydroxymaleimido derivatives. The combination is stirred for a two day
period. The mixture is then chromatographed on a preparative TLC plate
followed by elution with 15% MeOH/CH.sub.3 Cl to produce the compound of
General Formula I.
Alternatively, the product of General Formula I wherein group Y is nothing
and group R is a reactive ester may be prepared by dissolving a
sulforhodamine 101-4-sulfonyl chloride in dry DMF and a pH 8.5 sodium
carbonate solution containing a terminal amine substituted carboxylic acid
of the general formula, H.sub.2 NXCOOH, in HCl, wherein X is selected from
an alkyl, a monocyclic aliphatic saturated hydrocarbon, or an aryl. The
mixture is stirred for one hour followed by evaporation of the volatile
solvents. The residue is partitioned between CH.sub.3 Cl/H.sub.2 O (pH 4)
to remove the sulfonic acid. The organic layer is dried and evaporated.
The product is dissolved in DMF and pyridine is added. To the solution is
added a succinimdyl ester of the formula:
##STR10##
wherein R' is consists of an N-hydroxysuccinimido derivative. The
combination is stirred for a two day period. The mixture is then
chromatographed on a preparative TLC plate followed by elution with 15%
MeOH/CH.sub.3 Cl to produce the compound of General Formula I.
EXAMPLE I
Preparation of an Amine Reactive
Sulforhodamine 101 Labeling Reagent of General Formula I
The synthesis of an amine-reactive sulforhodamine 101 labeling reagent of
General Formula I is outlined in FIG. 1. In the initial step of the
synthesis, sulforhodamine 101 (0.50 g, 6.5% water) was dried overnight at
100.degree. C. under high vaccuum. The resulting dried powder is mixed
with 3.0 mL of freshly distilled phosphorous oxychloride. The mixture is
stirred slightly overnight. The phosphorous oxychloride is then removed at
a vacuum pump to dryness. The sulforhodamine 101 is then dissolved in
10-20 mL of dry dimethyl formamide (DMF).
1,2-diaminoethane (5.14 mL) is separately mixed in a 100 mL flask with 25
mL of dry DMF. The sulforhodamine 101/DMF mixture is then added dropwise
to the diamine mixture with vigorous stirring. The solution is then
allowed to stir for 15 minutes. The solvents are then evaporated at the
pump to dryness, and the residue is taken up in a few milliliters of
methanol and partitioned between water and chloroform in a separatory
funnel. The water layer is extracted three times with chloroform and the
organic extracts are combined, dried (Na.sub.2 SO.sub.4), evaporated, and
pumped dry to give the crude amine.
The crude amine is dissolved in 5 mL of cloroform and developed on two
preparative TLC plates (1 mm thickness). After separation of the bottom
amine band from the plate, the adsorbent is extracted four times with
methanol and once overnight. The extracts are combined, reduced in volume,
and poured into water. Upon extraction with chloroform, the dye solution
is dried, filtered, evaporated, and pumped dry to yield a sulforhodamine
101 sulfonylethylenediamine, 0.15-0.18 g (30-36%). Purer samples can be
obtained by dissolving the amine in chloroform and precipitating with
hexane.
Disuccinimdyl glutarate (0.6 g) in dry DMF (20 mL) under vigorous stirring
is subjected to the inverse addition of a solution consisting of 140 mg of
sulforhodamine 101 sulfonylethylenediamine (0.216 mmol) in 40 mL of dry
DMF over 10 minutes. The sulforhodamine 101 sulfonylethylenediamine/NHS
ester solution is stirred for 15 minutes then evaporated in vacuo. The
residue is taken up in about 10 mL of dry chloroform and applied to four
preparative TLC plates (1 mm thickness) with 15% MeOH/CHCl.sub.3 as the
eluant. The portion of the plate containing the product is removed and
quickly exhaustively extracted with 15% MeOH/CHCl.sub.3. If the analytical
TLC test shows that the product solution is contaminated with
disuccinimidyl glutarate, the combined product solutions are evaporated
and again chromatographed on a single preparative TLC plate and worked up.
Upon obtaining a satisfactory product, the 15% MeOH/CHCl.sub.3 solution is
evaporated and the residue is dissolved in ethanol-free chloroform. The
mixture is filtered, evaporated, and pumped dry to yield the product of
General Formula I approximately 110 mg (54%).
.sup.1 H NMR (CDCl.sub.3) (500 MHz) (major isomer--4-sulfonamide) 8.75 (d,
1H, J=0.5 Hz, aromatic 3-H), 8.01 (dd, 1H, J=3, 1 Hz, aromatic 5-H), 7.61
(br s, 1H, amide H), 7.22 (d, 1H, aromatic 6-H), 6.84 (s, 2H, aromatic 1,
5-H), 3.34 (m, 8H, NCH.sub.2), 3.27 (m, 2, SNHCH.sub.2), 3.13 (m, 2,
CH.sub.2 NCO), 2.91 (m, 4H, ax. benzyl CH), 2.77 (s, 4H, NHS-H), 2.63 (m,
4H, eq. benzyl CH), 2.53 (t, 2H, CH.sub.2 COONHS), 2.25 (t, 2H,
NHCOCH.sub.2), 2.20-1.80 (m, 10H, --CH.sub.2 --); R.sub.f =0.53 (silica,
15% MeOH/CHCl.sub.3).
It is believed that the product of General Formula I, with the substituted
4-sulfonyl group, exists as an isomer, in at least a two to one ratio with
the substituted 2-sulfonyl group.
Experiments have been performed that show that the compounds of the present
invention can be reacted more controllably with a ligand (e.g., an
antibody) than Texas Red. For example, these experiments demonstrate that
the present invention reacts controllably with an antibody allowing
consistent substitution ratios depending on the input ratios, while Texas
Red produces more variable results, in some cases binding too many
fluorophores to the antibody thereby tending to destroy the antibody's
ability to bind to its target antigen. The present invention provides a
more controllable substitution range over Texas Red.
In the preceding detailed description, the invention is described with
reference to specific exemplary embodiments thereof. It will, however, be
evident that various modifications and changes nay be made thereto without
departing from the broader spirit and scope of the invention as set forth
in the claims. The specification and drawings are, accordingly, to be
regarded in an illustrative rather than a restrictive sense.
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